1. Field of the Invention
The invention concerns the display of information in a digital computer system and more particularly concerns the display of information about a very large number of entities.
2. Description of the Prior Art
A major problem for users of computer systems is that displays of information accessible through the computer system generally provide either a very high level view of the information or a very detailed view of the information, while the user often needs a view of the information which is at an intermediate level. For example, text files are represented in their entirety by icons or file names, and once a text file has been selected, a number of lines in the file can be displayed in a window. There is, however, no display of information which gives a reasonable idea of how the lines presently displayed in the window relate to the lines in the entire file. One consequence of the lack of such an intermediate level of display information is that it becomes difficult to use and understand available information. For instance, many programming projects maintain a change data base which contains information about the changes made on the source code of a computer program. It is possible to determine from the data base when each line of the source code was changed, but the prior art has provided no way of giving the programmer an overview of the relationship between the changes and the files containing the source code. Answering a question such as what other lines of source code were changed when a given line was changed becomes very laborious, and even when the question is answered, it is answered in such a way that the programmer often cannot appreciate the significance of the answer.
One attempt to provide a low level of intermediate level of information has been the scroll bar. Many text editors provide a scroll bar at one side or the other of the window in which the text being edited appears. The scroll bar represents the entire text, and by positioning the cursor in the scroll bar, one can move to a corresponding point in the text. For example, if one moves the cursor to a point 1/2 way down the scroll bar, the text which appears in the window is centered on the line which is half way through the document. In some scroll bars, there is further a change in appearance of the part of the scroll bar which corresponds to the portion of the document currently being displayed in the window, so that the user can, by looking at the scroll bar, determine where the displayed portion is relative to the entire text.
The scroll bar has further been used to provide a somewhat more detailed level of some kinds of intermediate information. William C. Hill, James D. Hollan, Dave Wroblewski, and Tim McCandless disclose a system in their article "Edit Wear and Read Wear: Their Theory and Generalizations", Software Production Research, in which the scroll bar includes histograms showing how often individual lines of a document have been edited or read. The addition of histogram information to the scroll bar is a specific example of a general technique termed attribute mapped scroll bars which is disclosed in two U.S. patent applications: Wroblewski, Hill, McCandless, Attribute-enhanced Scroll Bars, U.S. Ser. Nos. 07/523,117, filed May 14, 1990, and 07/626,130, filed Dec. 11, 1990. While useful, attribute mapped scroll bars provide an intermediate level of information only if the information is present. They do not solve the general problem of showing intermediate structures such as text lines or data records which are always present in the files or data bases being displayed. It is an object of the apparatus and techniques disclosed in the following to solve this and other problems of information display in computer systems.